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SubjectRe: [PATCH] vfs: Fix possible NULL pointer dereference in inode_permission()
On Thu, 9 Jan 2014 18:25:23 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 10 Jan 2014 06:41:03 +0800
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> > I think the sane short term fix is to make the kfree() of the i_security
> > member be a rcu free, and not clear the member.
>
> You mean my first patch?
>
> https://lkml.org/lkml/2014/1/9/349
>

Oh wait, you said not to clear the member. Thus, the patch would look
like this:

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Index: linux-trace.git/security/selinux/hooks.c
===================================================================
--- linux-trace.git.orig/security/selinux/hooks.c
+++ linux-trace.git/security/selinux/hooks.c
@@ -234,6 +234,14 @@ static int inode_alloc_security(struct i
return 0;
}

+static void inode_free_rcu(struct rcu_head *head)
+{
+ struct inode_security_struct *isec;
+
+ isec = container_of(head, struct inode_security_struct, rcu);
+ kmem_cache_free(sel_inode_cache, isec);
+}
+
static void inode_free_security(struct inode *inode)
{
struct inode_security_struct *isec = inode->i_security;
@@ -244,8 +252,7 @@ static void inode_free_security(struct i
list_del_init(&isec->list);
spin_unlock(&sbsec->isec_lock);

- inode->i_security = NULL;
- kmem_cache_free(sel_inode_cache, isec);
+ call_rcu(&isec->rcu, inode_free_rcu);
}

static int file_alloc_security(struct file *file)
Index: linux-trace.git/security/selinux/include/objsec.h
===================================================================
--- linux-trace.git.orig/security/selinux/include/objsec.h
+++ linux-trace.git/security/selinux/include/objsec.h
@@ -38,7 +38,10 @@ struct task_security_struct {

struct inode_security_struct {
struct inode *inode; /* back pointer to inode object */
- struct list_head list; /* list of inode_security_struct */
+ union {
+ struct list_head list; /* list of inode_security_struct */
+ struct rcu_head rcu; /* for freeing the inode_security_struct */
+ };
u32 task_sid; /* SID of creating task */
u32 sid; /* SID of this object */
u16 sclass; /* security class of this object */

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